The present invention relates to a new and improved method of treating short fiber fractions after separating the long fiber fractions from a secondary fiber mixture, especially for the fabrication of cardboard folding boxes.
When fabricating cardboard folding boxes it is conventional practice to use for the most part secondary fibers. These secondary fibers constitute fibers which are obtained upon processing waste paper. This fiber mixture composed of long and short fibers is subdivided into a long fiber fraction and a short fiber fraction by a fractionating machine working with screens. The long fiber stock is used in the cover layers and the short fiber stock in the inserts or liners of the cardboard.
During the preparation of the long fiber stock for the cover layers there should be obtained an increase of the strength properties, preferably the modulus of elasticity. It is for that reason that the long fibers are thermally treated in a process stage and thereafter or also simultaneously mechanically processed in a disperger. During this mechanical disperging process there is realized, apart from improved strength, also a disperging of disturbing wax agglomerates so that they are no longer optically disturbing. The comminuted particles bind at the surface of the long fibers so that they adhere thereto during processing. In this way the long fiber stock is free of disturbing wax particles.
As to the short fiber stock used for the inserts of liners the processing operation is less concerned with the strength properties of the short fibers as opposed to the specific volume which should be as large as possible in the product produced therefrom. As to the expression "specific volume" such is the volume related to the weight.
The short fiber fraction which is obtained from the fractionating machine--in this case the fractionating operation is accomplished in a fiber fractionator--is delivered as obtained to the papermaking machine after undergoing several cleaning and thickening steps. This technique is not satisfactory. It has been found that in the finished product there can be discerned disturbing wax spots or speckles and that these wax spots emanate from wax particles of the waste paper and which are introduced into the product by means of the short fiber fraction. It also has been found that a sorting out of the disturbing wax particles with screen sorters is not possible.
In this case it does not appear to be advantageous to accomplish a hot disperging operation, such as employed for the long fiber fraction, since a great deal of energy would then be required as also a rather extensive equipment expenditure. Additionally, such is in contradiction to the purpose of the treatment since there is lost the desired as large as possible volume of the short fiber stock.